Exemplary devices in automated production- and testing systems include balances of a modular configuration—so-called weighing modules—particularly well suited to be integrally incorporated into these systems. In essence, the balances used for this purpose are of the type where the indicator unit is arranged separately from the balance, for example in a system with a central indicator unit for a plurality of weighing modules. Instead of being presented through an indicator, the weighing results can also be delivered from the weighing modules to a process control system. Integrated weighing modules of this kind are used in systems for the production and testing of small and relatively expensive parts, for example in filling- and packaging machines for tablets, capsules, ampoules, etc. in the pharmaceutical industry, or in the checking of ball bearings.
In cases where speed is important in measuring the individual masses of weighing objects, an arrangement of a plurality of weighing modules suggests itself, for example to allow the individual masses of weighing objects of the same kind to be measured in parallel. Since a conveyor device such as a robotic arm with multiple grippers is normally used to put the weighing objects in parallel onto the individual load carriers of the weighing modules and to remove them from there after they have been weighed, the positions of the individual load carriers in relation to each other and in relation to the conveyor device have to be accurately and durably set.
Devices which are used for weighing substantially uniform weighing objects belong to the known state of the art. Predominantly, these devices are arrangements of weighing modules in rows or two-dimensional arrays. Other arrangements are based on the concept of placing the weighing modules in a star-like arrangement around a row arrangement of load carriers which have to be matched to the distances between the delivery elements of an—in most cases existing—conveyor device, because the weighing module is often too large to allow an arrangement at the required close intervals.
A row arrangement of weighing modules is disclosed in DE 102 42 118 A1 and DE 199 20 494 A1, wherein four weighing modules are arranged in a row in an apparatus for weighing pharmaceutical receptacles, in particular ampoules, wherein before and after the filling the receptacles are brought to and removed from the weighing modules by means of a gripper device.
A two-dimensional arrangement of weighing cells is disclosed in JP 01 212327 A, which describes a cost-effective method of producing a large number of weighing cells from a plate of spring material to which strain gauges are bonded as sensor elements.
Disclosed in US 2003/0218467 is a matrix array of microbalances which can be used with preference in the field of combinational chemistry for the determination of masses or mass changes in the microgram range. Each of the individual microbalances has a mechanical resonator as a sensor whose resonance behavior correlates to a mass or a change in the mass detected by the sensor.
A two-dimensional star-shaped arrangement of weighing modules is disclosed in U.S. Pat. No. 6,615,638 B1, which finds application in a calibration device for multi-channel pipettes. This arrangement is suitable for matching the distances between the load carriers, each of which belongs to one of the weighing modules, to the tips of the multi-channel pipette that is to be calibrated. The weighing receptacles, each of which is filled with the calibration liquid dispensed from one of the channels of the multi-channel pipette, can thus be weighed simultaneously, although the dimensions of the weighing modules which function according to the principle of electromagnetic force compensation are larger than the distance interval that the load carriers need to conform to.
The state-of-the-art microbalances as described in US 2003/0218467 have a disadvantage that, while being suitable for applications where masses in the microgram range need to be determined, they are not, for example, suited for the range of milligrams to grams. In the case of weighing modules with large dimensions in comparison to the distances between the delivery elements of a conveyor device, even the star-like arrangement disclosed in the state of the art does not satisfy the requirements when a complex conveyor device is used, in particular of a type that is equipped with a two-dimensional arrangement of delivery elements. Since the dimensions of the weighing modules in length as well as width are often larger than the required distance between the central lengthwise axes of the load carriers, only a limited number of weighing modules can be placed around a provided area that is predetermined by the delivery elements of the conveyor device.